Contact start plasma arc torches generally do not require the torch to contact the metal workpiece being cut or welded by the torch at the time the plasma arc is initiated. Contact start plasma torches can include “blow back” cutting torch technologies, which are described in U.S. Pat. No. 4,791,268 and U.S. Pat. No. 4,902,871, the contents of which are incorporated herein by reference in their entirety. The contact start plasma torch can include an electrode (e.g., cathode) that can move axially within the torch body under the influence of a spring, and gas forces that oppose the spring. The gas forces can act on lower surfaces of the electrode adjacent the anode, such as the torch nozzle. During torch start up, a gas pressure in the region between the electrode and the anode can build to a sufficient level to lift the electrode against the spring, this separation igniting the plasma arc. When cutting is stopped and the gas flow is terminated, the spring biases the electrode to a position in which it contacts the nozzle and seals off the plasma exit port in the nozzle.
Plasma arc torches using “blow forward” technologies are also described in U.S. Pat. Nos. 5,994,663, 5,897,795, and 5,841,095, the contents of which are also incorporated herein by reference in their entirety. All of these patents are assigned to Hypertherm, Inc. of Hanover, N.H., the owner of the present invention.
During torch operation, torch consumables (e.g., the electrode, nozzle, and shield) are exposed to high temperatures. The torch consumables can be cooled utilizing various techniques, such as utilizing water injection cooling to cool the nozzle and/or shield, utilizing liquid cooling in the electrode and/or about nozzle, or utilizing vent holes to cool the shield which is described in U.S. Pat. No. 5,132,512, the contents of which are also incorporated herein by reference in their entirety and which is assigned to Hypertherm, Inc. of Hanover, N.H., the owner of the present invention.
One area for improvement to the plasma arc torches relates to cooling consumables for the plasma arc torch (e.g., electrode, nozzle, and shield). Cooling capacity has been a limitation of previous designs relating to plasma arc torches. For example, previous designs have required the use of cooling mediums other than or in addition to a gas (e.g., cooling water or liquid) for torches that operate at high (e.g., 100 or 200 Amps, or more) current levels.
Unfortunately, most of these cooling methods can require cooling systems external to the torch (e.g., which can include water supplies, reservoirs, heat exchange equipment, supply pumps, etc.). External cooling systems can increase the associated equipment expense, can require more maintenance, be vulnerable to spills, and in some cases, can require disposal of the cooling medium. The issue of cooling the plasma arc torch is more acute for higher current systems, as higher current systems can generate more heat and have larger cooling demands. Indeed, commercially available plasma arc torch cutting systems operating at more than about 100 amperes utilize cooling systems using a liquid coolant (e.g., water or glycol). However, as explained above, these systems all suffer from the cost and maintenance issues associated with such systems.
It is therefore an object of this invention to provide a cooling system, process, and related components for a plasma arc torch that avoids these drawbacks.